Cytokines are protein mediators that play a part in inflammation, the immune response, cell growth, repair, and fibrosis. All of these are continuing processes in active rheumatoid arthritis (RA), and so it would be expected that many cytokines would be actively produced in RA joints. Here, the molecular strategies devised to study the possible role of cytokines in the pathogenesis of RA, are reviewed and some of the initial results described. The relative abundance of various cytokines is 'catalogued' and then attention is turned to an attempt to discover which cytokines are of major importance in the pathogenesis. Neutralising antibodies to cytokines were used for that purpose, and it was found that tumour necrosis factor alpha (TNF alpha) is one of the major signals regulating the production of interleukin-1 in the RA, but not in the osteoarthritic joint. To understand further the dynamics of the cytokine network localisation of the cytokine producing cells by immunostaining--for example, TNF alpha, is currently being established.